30 Years of Commercial Components In Space: Selection Techniques without Formal Qualification

From the earliest pioneering scientific missions to the sophisticated small satellite programmes of today there has been a continuity in the use of commercial-off-the-shelf (COTS) components. Recent advances in VLSI electronic components has accelerated their use in small satellite programmes, significantly contributing towards a \u27faster, cheaper and arguably better\u27 approach to space missions. Such applications however, in combination with the fundamental inconsistencies of COTS heritage require some differing techniques to those of the established space engineering regimes. Furthermore, the rapid development cycle of modem microelectronics devices and their packaging profiles for the commercial and domestic markets constitute a radical departure from the assurance base offered by the now dwindling Mil Standard component lines. This paper presents a summary of techniques employed during 30 years of designing space hardware systems during which an increasing proportion of COTS general electronic components have been utilised. It describes techniques that have been undertaken within small/medium-sized organisations producing research instrumentation and microsatellite platform systems where conventional component qualification by long-term environmental test regimes is unavailable. Results from the long established University of Surrey (UK) small satellite programme are used to support this regime and provide good indicators of reliability and failure mechanisms. The data comes from the 15 small satellites using Surreys bus design that have been launched to date and have now accumulated more than 70 orbit-years operation in LEO. A total engineering philosophy has evolved addressing the many different issues that are relevant to COTS usage. Essential elements include, a component selection processes with verification of their suitability for space applications; a hardware design concept that reflects system reliability requirements; addressing the more essential bus services with higher levels of partial or full redundancy and a conservative design change cycle that utilises components with an established pedigree. This philosophy relies on sound engineering practice whilst ensuring that the specified quality of a component is not given a completely inappropriate status. Factors such as component handling, board level design, build quality, sub assembly compatibility, system structure, interconnection techniques and modes of operation are all factors of the total reliability. The ultimate test is long term exposure to the space environment and this paper details the results to date from the Surrey programme. The conclusion of this work is that the component selection and usage regime provides a viable alternative to that of conventional qualification methods and if this regime is fully adopted will provide predictable results